A data format of music sequence data represents a music piece and enables a compatible sound generating apparatus to reproduce the music piece at a first quality while allowing a non-compatible sound generating apparatus to reproduce the music piece at a second quality different from the first quality. The music sequence data is composed of event data and timing data. The event data represents various types of musical events occurring during the course of reproducing the music piece. The timing data specifies occurrence timing of each musical event. The event data representing at least one type of the musical events is scrambled such as to affect performance of the non-compatible sound generating apparatus without affecting performance of the compatible sound generating apparatus, so that the compatible sound generating apparatus can maintain the first quality of the music piece even when the music piece is reproduced from the music sequence data containing the scrambled event data, while the non-compatible sound generating apparatus cannot maintain the second quality of the music piece when the music piece is reproduced from the music sequence data containing the scrambled event data.